Shirred food casings of flexible tubing are commonly used in the food industry for making and processing various encased food products such as frankfurters, sausages, or the like. Consequently, shirred casings, the methods of making the casing materials, casing shirring methods, shirred tubular casing articles or "sticks", and the apparatus and methods relating to the use of the shirred casing to produce a stuffed food product, are all well known in the art. For example, a shirred casing, a shirring method and apparatus are described generally in U.S. Pat. No. 2,984,574. U.S. Pat. No. 3,115,668 describes a machine for stuffing a shirred casing stick to make linked sausages or frankfurters. Recently, "large size" casing sticks have been mounted on support tubes for the purpose of providing a coherent stick that can be compressed to provide increased casing length for a given stick length, as described in U.S. application Ser. No. 363,851.
The advent of automatic machines for stuffing and/or linking of shirred food casings as described, for example, in Townsend U.S. Pat. No. 3,115,668, has greatly increased the production rate of sausage type products. In an automated stuffing operation, as described in the Townsend Patent, hollow shirred casing sticks are fed automatically and rapidly onto the stuffing horn of the stuffing machine. The horn axially picks up the stick by extending through the bore of the hollow stick to the fore end of the stick. The horn then advances the stick into a chuck. The chuck grips the fore end of the stick and rotates the stick about the horn during the stuffing operation to link the stuffed casing.
In order for the horn to advance the stick into the chuck, the bore of the stick at the fore end must be plugged. With the bore plugged in this fashion, the stuffing horn can push on the plug from inside the stick until the fore end is firmly gripped by the chuck. The stuffing horn continues to advance into the chuck, and this moves the plug out of the bore of the shirred stick and deshirrs a portion of the casing from either the fore end of the stick or from the plug at the start of the stuffing cycle.
Another function of the plug is that it seals the casing end to block flow of the emulsion being stuffed in the initial stage of the stuffing operation and prior to the formation of the first link. In this respect, emulsion forces the casing of the plug into the linker so that flow of the emulsion out of the casing is restricted until the first link is formed yet the emulsion is easily strippable in a subsequent operation as described hereinbelow.
Providing a casing stick having a plug or closure formed at one end, generally, can be more uniformly and economically accomplished during the manufacturing of the shirred casing stick than during use of the casing. To this end, various types of casing closures and methods for forming such closures are known in the art. For example, Townsend, U.S. Pat. No. 3,162,893, discloses a casing end closer which engages the terminal end pleats of the shirred casing and rotates to twist the casing tightly upon itself to form, as Townsend describes, a closure "having a knot-like neck". Other end closures are formed by pinching and twisting end pleats of the casing as in U.S. Pat. No. 3,882,252 and Canadian Pat. No. 813,838. End closures can also be formed within the hollow stick or formed outside the stick and subsequently inturned or implanted within the stick. For example, Alsys, U.S. Pat. No. 3,274,005 discloses a shirred casing having an end which is twisted closed outside the hollow stick and then pulled into a position within the bore of the shirred casing. A second Alsys U.S. Pat. No. 3,383,222 discloses a shirred casing having a compressed plug end closure implanted in the fore end of the stick. Here the plug is formed by pulling a strand of the casing laterally across the bore of the stick to form a blind, inturning the strand into the end of the casing stick and then forming the inturned strand into a plug by axially compressing the inturned strand against a fixed surface with a plunger inserted into the other end of the casing stick. Because the formation of the blind in this patent involves the asymmetrical stretching of unshirred casing across the bore of the stick, the resulting plug is asymmetrical relative to the axis of the stick bore.
In Tums, U.S. Pat. Nos. 3,865,954, 3,914,447 and 4,070,729 there are disclosed, respectively, a hollow casing stick having an end closure, a method, and a device for forming the end closure, wherein the closure is a progressively twisted, close packed knot implanted within the bore of the shirred stick. The Tums closure is formed by twisting terminal pleats of the shirred stick about a rod inserted within the bore of the shirred stick. Sheridan et al., U.S. Pat. No. 3,892,869, discloses a floating end closure formed within the shirred stick from a predetermined amount of casing material that has been inturned into the bore of the shirred stick and axially compressed. The resulting closure is asymmetrical relative to the stick bore.
In U.S. Pat. No. 4,075,938, the end closure is formed within the casing stick by first winding a deshirred portion of the casing to form a wall portion across the bore of the stick. The winding mechanism, including a rotating mandrel, is then advanced into the bore of the casing stick. This advances the wall portion into the bore while simultaneously winding deshirred casing on the rotation mandrel to form a generally cylindrically twisted or radially wound portion following the advancing wall portion.
A further, twisted, implanted closure is disclosed in German Patent Application Ser. No. P 29 26543.8 published on Jan. 22, 1981. Here the winding mechanism is moved axially away from the end of the stick as it is rotated so that the casing material can be twisted between 20 and 30 revolutions without tearing the casing material. The twist closure of casing material formed by these rotations is then pushed axially to move it into the bore of the stick.
Other end closures formed within the shirred stick by crimping an end of the stick are shown in Matecki, U.S. Pat. Nos. 3,419,401; 3,550,191; 3,564,647; and 3,570,045. End closures formed outside the bore of the stick and subsequently implanted are shown in U.S. Pat. Nos. 3,942,568; 3,942,569; and 3,971,301.
One long-standing commercial problem with conventional shirred sticks having an end closure at one stick end, such as those described above, relates to air entrapped within the stick bore between the last-to-be-stuffed end of the shirred stick and the end closure implanted in the bore at the first-to-be-stuffed end of the stick. In some cases, during loading of these sticks onto a stuffing horn at the start of a stuffing operation, the entrapped air in the stick bore between the last-to-be-stuffed end of the stick and the end closure becomes compressed. This compressed air is the source of a variety of problems during the stuffing operation, ranging from blown end closures and bursting of the casing to an undersized first several links stuffed from the shirred stick.
A prior art solution to the above compressed air build-up problem involves the use of a "vented" end closure, i.e., an end closure having a hole in it to convey air out of the shirred stick. Although vented end closures solve the compressed air problem, vented closures sometimes cause another problem, namely, food product waste due to leakage out of the end closure vent.
Heretofore, there has been a long-felt need for avoiding or reducing the compressed air build-up problem without food product leakage and waste.